What, literally, makes us laugh?

Dear Cecil: Upon rare occasions when there is a funny commercial on TV, if I give in to laughter I experience a short-term case of retrograde amnesia, just long enough to make me forget what the product was. This has also been the fate of some of the funniest jokes and scenes that have come my way. It seems that the harder I laugh, the less info I can retrieve. It turns out I’m not the only one, which brings me to ask, JUST WHAT IS THE LAUGHTER NEUROTRANSMITTER??? It derails the habitual circuit patterns of the brain, alleviates stress, lowers blood pressure, and gives the brain a buzz. How and where is this transmitter synthesized? What co-factors and nutrients have to be present to make it? Is there a humor enzyme? Shan G., Venice, California

Cecil replies:

Dear Shan:

If it’s knowledge you hunger for, lad, chew on this from the December 7, 1984 Journal of the American Medical Association:

“Although there is no known `laugh center’ in the brain, its neural mechanism has been the subject of much, albeit inconclusive, speculation. It is evident that its expression depends on neural paths arising in close association with the telencephalic and diencephalic centers concerned with respiration. Wilson considered the mechanism to be in the region of the mesial thalamus, hypothalamus, and subthalamus. Kelly and co-workers, in turn, postulated that the tegmentum near the periaqueductal gray contains the integrating mechanism for emotional expression. Thus, supranuclear pathways, including those from the limbic system that Papez hypothesized to mediate emotional expressions such as laughter, probably come into synaptic relation in the reticular core of the brain stem. So while purely emotional responses such as laughter are mediated by subcortical structures, especially the hypothalamus, and are stereotyped, the cerebral cortex can modulate or suppress them.”

I hope this clears things up.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.